<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .current {
            background-color: orange;
        }
    </style>
</head>

<body>
    <p>0</p>
    <div class="J_calculator">
        <div class="result">0</div>
        <div class="input-group">
            <input type="text" value="0" class="f-input">
            <input type="text" value="0" class="s-input">

        </div>
        <div class="btn-group">
            <button data-field="plus" class="current">+</button>
            <button data-field="minus">-</button>
            <button data-field="mul">*</button>
            <button data-field="div">/</button>
        </div>
    </div>
    <script src="././js/test.js"></script>
</body>

</html>